It has been the opinion of experts skilled in the art that the cross-section of the legs and pole pieces from the location of abutment of the permanent magnet on the core of the electromagnet to the pole faces of the pole pieces of the magnet arrangement must be so dimensioned that when the magnetic flux of the permanent magnet and the magnetic flux of the fully energized electromagnet are superimposed on each other in these sections of the magnetic flux path magnetic saturation of the material will not be exceeded. If one is to cling to this opinion electric energy may be saved when energizing the electromagnet by additionally using a permanent magnet, but the quantity of material required for obtaining a desired magnetic flux as well as the size and weight of an electric device or machine provided with such a magnet arrangement cannot be reduced.
It is the objective of the invention to avoid this drawback of the known magnet arrangement. Tests carried out by applicant have surprisingly shown that the combined magnetic fluxes of the permanent magnet and the electromagnet can also be utilized without drastically increasing the cross-sections of the legs and pole pieces of the magnet arrangement, and consequently the invention essentially resides in that the cross-section of the pole pieces is smaller than the sum of the cross-section required for conducting the magnetic flux of the fully energized electromagnet alone at saturation and the cross-section required for conducting the magnetic flux of the permanent magnet alone at saturation.
The effect obtained by the invention, which contradicts a long-standing preconceived idea of the experts in the field, has not yet been fully explained physically.
The invention magnet arrangement can be used in all electromagnetic devices and electric machines wherein a magnetic field with high values of flux density is required, particularly if the magnetic field is to be periodically variable between zero and a maximum value.
In rotating electric machines the invention can be utilized in the stator and in the rotor or only in one of the two parts.
The invention may further be applied in electromagnetic devices such as lifting magnets, relays and magnetic separators for retaining and separating ferromagnetic particles from fluids.
An economical embodiment of the invention device or machine is obtained when the cross-section of the pole pieces is approximately equal to the cross-section required for conducting the magnetic flux of the fully energized electromagnet alone or of the permanent magnet alone at saturation.
The most pertinent prior art related to the background of this invention is disclosed in U.S. Pat. Nos. 4,064,442 and 4,132,911.